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Letter to The Editor

Dear Irwin,

I have read with great interest your article ‘Towards Wookey Hole’ (first part).  I think the Dining Room Dig is a good bet.

If this passage goes up and down again beyond the sump it will confirm to the Swildons Hole by-passes and be what the Poles called a ‘corkscrew’ passage working up from a clay choked stream way to rejoin it later. (Thousands of years in the process). Once completed and rejoined to the stream beyond the sump, there will be a strong flow along the corkscrew passage until a sucking action by the sump it is cleared.  So don’t be dismayed if you find that the passage jinks about a lot with right-angle bends according to the jointing.  There should be flow markings on the walls and the directions of your digs should follow the indicated current direction all the way, and if necessary dig a window to the wall at intervals to see the marking.

The ‘rock pendants’ near the roof are probably due to seepage water working down at the top of the clay fill after the passage was choked.  This may indicate an aven or open joint etc. opening to the top of the passage.

I find the best way to test current markings which are faint is with the fingertips.  Rubbing gently in direction of flow gives the feel  of a slight edge down, then a smooth section and another edge down, and the opposite of course against the flow direction. With a torch, with a narrow beam, shine it against the current direction to get narrow brighter lines, but none if you shine it in the other direction.

Use candles to detect bad air, one placed ahead of the dig i.e. in the air space above the clay and others further along the passage.  NO ACETYLENE LAMPS.  Electric torches for good viewing.   If you are digging in a rising and there is a ‘pool’ of CO2 further on the routine of digging and passing clay down the open part may act like a pump and drag bad air down the excavated passage.  I found this in a dig in India – working up a clay filled passage from draughty, well ventilated passage below.  After about 45 feet, the dig sloping up the passage levelled off and then dipped gently into a wider area.  It was quite sinister to see the candles ahead go out, then 10 seconds later the one just behind me and 20 seconds later another at a bend would go out!  Then, the digging party would go out and return in ten minutes or so.  After a couple of more digs like that the dig was abandoned.  The floor beyond was a circular basin of clay evidently full of CO2 and no continuing passages.  I have met with pools of CO2 on many occasions and great care is need in any dig.

Yours sincerely
E.A. Glennie (C.R.G.)